Cooling Fan Having a Radial-Air-Gap Motor and a Method for Determining the Dimensional Proportion of the Motor

ABSTRACT

A cooling fan having a radial-air-gap motor is disclosed. The cooling fan includes a fan frame, an impeller and a stator assembly. The fan frame has a shaft-coupling portion. The impeller has a hub, a shaft and a plurality of blades. The blades are arranged on an outer periphery of the hub. At least one magnetic element is arranged on an inner periphery of the hub. There is a height between a bottom face of the shaft-coupling portion and a top face of the hub. There is a maximum thickness between the bottommost and uppermost faces of the magnetic plate unit. A ratio of the maximum thickness to the height is between 0.1 and 0.6. A method for determining the dimensional proportion of the motor is also disclosed. The method selects a ratio of a maximum thickness to a height as 0.1 to 0.6.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a cooling fan and a method for determining the dimensional proportion of the motor of the cooling fan and, more particularly, to a slim cooling fan that has a reduced thickness and is equipped with a radial-air-gap motor, as well as a method for determining the dimensional proportion of the motor.

2. Description of the Related Art

In recent years, since the modern electronic products are miniaturized and have high performances, electronic elements inside the electronic product are liable to generate a large amount of heat during the operation of the electronic product. As a result, the heat of the electronic product cannot be expelled smoothly, especially in the small interior space of the electronic product. Disadvantageously, the performance of the electronic product is not stable or is even deteriorated, affecting the reliability of the electronic product. Thus, the heat dissipation has become an important issue when designing any electronic product.

Generally, a cooling fan is used in an electronic product for cooling purposes. The cooling fan operates to drive the air to flow, so that the heat in the electronic product can be expelled. Furthermore, a slim cooling fan is often used in a compact electronic product. The slim fan may have a height of for example, 2 mm to 4.5 mm measured from the bottom face of the shaft-coupling portion of the fan frame to the top face of the hub of the impeller. Furthermore, for any slim fan that has a radial air gap between the stator and the rotor, although it has been attempted to reduce the height of the fan as much as possible when designing the fan, the motor that is equipped with the fan can have inadequate performance if the stator and the rotor of the fan do not have sufficient magnetic-inducting areas therebetween. Thus, the performance of the fan should be taken into consideration when trying to reduce the height of the fan.

Conventionally, the dimensions of the motor and the fan frame are determined according to the designers' experiences or the trial and error method. After the dimensions of the motor and the fan frame are determined, the motor is installed in the fan frame to test the performance of the fan. If the performance of the fan does not meet the required level, the dimensions of the motor and the fan frame are changed and the fan is tested again under the modified dimensions. The procedure is repeated until the performance of the fan meets the required level. Since there is no rule to be followed when determining the dimensional relation between the motor and the fan frame, it usually takes a large amount of time and effort to design the fan.

In light of this problem, a fan is disclosed by China Patent No. 101113737 entitled “FAN AND A METHOD FOR DETERMINING THE MOTOR SIZE OF THE FAN”, as shown in FIG. 1. Fan 9 includes a fan frame 91, an impeller 92 and a motor 93. Impeller 92 is installed in fan frame 91. Motor 93 includes a rotor assembly 931 and a stator assembly 932. Stator assembly 932 is able to drive rotor assembly 931 to rotate, thereby driving impeller 92 to rotate. As such, the rotating impeller 92 drives air to flow. Assume stator assembly 932 has a diameter (X) and fan frame 91 has a width (Y), the relation between (X) and (Y) is defined as:

Y=13.25 X ^(1.4)±5%.

Furthermore, the ratio of (X) to (Y) is from 0.25 to 0.5. Based on this, the designer is able to correctly determine the dimensions of the fan frame and the motor, shortening the length of time in designing the fan and ensuring the performance of the fan.

However, the above formula is applicable only when the thickness of the fan is equal to or larger than 38 mm and the width (Y) of fan frame 91 is between 4 cm to 12 cm. In other words, the above formula is not applicable to the slim fan whose height is between 2 mm to 4.5 mm mentioned above. Although the width (Y) of fan frame 91 is one of the variables in the above formula, the configuration of fan frame 91 cannot be confirmed by the width (Y) of fan frame 91 alone. Thus, the above formula does not necessarily help in producing a fan with adequate performance.

SUMMARY OF THE INVENTION

It is therefore the objective of this invention to provide a slim cooling fan having a radial-air-gap motor wherein the fan structure is designed with a preferred dimensional proportion to ensure the ability of the fan to output a proper amount of air with proper air pressure. Thus, the performance of the fan is improved.

It is another objective of this invention to provide a method for determining the dimensional proportion of the motor's components. Based on the method, the cooling fan is able to output a proper amount of air with proper air pressure during the operation thereof.

In a preferred embodiment, a cooling fan having a radial-air-gap motor is disclosed. The cooling fan comprises a fan frame, an impeller and a stator assembly. The fan frame has a shaft-coupling portion. The impeller has a hub, a shaft and a plurality of blades. The shaft is connected to the hub and rotatably coupled with the shaft-coupling portion of the fan frame. The plurality of blades is annularly arranged on an outer periphery of the hub. At least one magnetic element is arranged on an inner periphery of the hub. The stator assembly has a magnetic plate unit. The magnetic plate unit has a face facing and spaced from the at least one magnetic element by the radial air gap. There is a height (A) between a bottom face of the shaft-coupling portion of the fan frame and a top face of the hub of the impeller along an axial direction. The height (A) is between 2 mm and 4.5 mm. There is a maximum thickness (B) between the bottommost and uppermost faces of the magnetic plate unit along the axial direction. A ratio of the maximum thickness (B) to the height (A) is between 0.1 and 0.6.

In a preferred form shown, the ratio of the maximum thickness (B) to the height (A) is between 0.2 and 0.4.

In the preferred form shown, the magnetic plate unit includes at least one magnetic plate.

In the preferred form shown, the magnetic plate unit includes a plurality of magnetic plates, and the maximum thickness (B) is a distance between a bottom face of the bottommost magnetic plate and a top face of the uppermost magnetic plate of the magnetic plate unit along the axial direction.

In the preferred form shown, the at least one magnetic element has a height along the axial direction smaller than or equal to a thickness of the magnetic plate unit along the axial direction.

In the preferred form shown, the magnetic element includes an outer circumferential face having a first central portion along the axial direction, and the magnetic plate unit includes an inner circumferential face having a second central portion along the axial direction. The first and second central portions are aligned with each other in a radial direction.

In another embodiment of the invention, a method for determining the dimensional proportion of a motor of a cooling fan having a radial air gap is disclosed. The method selects a ratio of a maximum thickness (B) of the motor to a height (A) of the motor as 0.1 to 0.6. The maximum thickness (B) is a maximum distance between the bottommost and uppermost faces of a magnetic plate unit of the motor along an axial direction, and the height (A) is a distance between a bottom face of a shaft-coupling portion of a fan frame of the motor and a top face of a hub of an impeller of the motor along the axial direction. The method further determines the value of one of the height (A) and the maximum thickness (B), and determines the value of the other one of the height (A) and the maximum thickness (B) based on the range of the ratio (B/A) and the previously determined value. Height (A) is between 2 mm and 4.5 mm.

In a preferred form shown, the range of the ratio (B/A) is 0.2 to 0.4.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 shows a conventional fan.

FIG. 2 is a cross-sectional view of a cooling fan according to a first embodiment of the invention.

FIG. 3 shows the performance diagram of the fan when the fan has different ratios (B/A) with the height (A) fixed at 4.5 mm.

FIG. 4 shows the performance diagram of the fan when the fan has different ratios (B/A) with the height (A) fixed at 2 mm.

FIG. 5 is a cross-sectional view of a cooling fan according to a second embodiment of the invention.

In the various figures of the drawings, the same numerals designate the same or similar parts. Furthermore, when the terms “first”, “second”, “third”, “fourth”, “inner”, “outer”, “top”, “bottom”, “front”, “rear” and similar terms are used hereinafter, it should be understood that these terms have reference only to the structure shown in the drawings as it would appear to a person viewing the drawings, and are utilized only to facilitate describing the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows a slim cooling fan having a radial air gap according to a first embodiment of the invention. The fan is comprised of a fan frame 1, an impeller 2 and a stator assembly 3. Both the impeller 2 and the stator assembly 3 are installed in fan frame 1. Stator assembly 3 is able to drive impeller 2 to rotate, thereby driving the air to flow. The fan may be an axial fan or a blower fan. In the embodiment, the fan is implemented as a blower fan, but is not limited thereto.

In FIG. 2, fan frame 1 includes a shaft-coupling portion 11. Impeller 2 includes a hub 21, a shaft 22, a plurality of blades 23 and at least one magnetic element 24. Shaft 22 may be rotatably coupled with shaft-coupling portion 11 of fan frame 1. Shaft 22 is preferably arranged at a center of hub 21 and has a length larger than a maximum axial thickness of stator assembly 3. The plurality of blades 23 is annularly arranged on an outer periphery of hub 21. Magnetic element 24 is arranged on an inner periphery of hub 21. Stator assembly 3 is coupled with shaft-coupling portion 11 of fan frame 1 and drives impeller 2 to rotate.

Specifically, stator assembly 3 includes a magnetic plate unit 31, an insulation sleeve unit 32 and a coil unit 33. Magnetic plate unit 31 includes at least one magnetic plate which may be made of material with magnetic conductivity. The magnetic plate may be a silicon steel plate, for example. In the embodiment, magnetic plate unit 31 may include a plurality of magnetic plates stacked together. Insulation sleeve unit 32 is arranged on two ends of magnetic plate unit 31. Coil unit 33 is an enamel copper wire wound around a predetermined part of insulation sleeve unit 32. The assembled components 31, 32 and 33 may be fitted around shaft-coupling portion 11, so that magnetic plate unit 31 and magnetic element 24 face each other while a radial air gap (G) is formed therebetween. As such, magnetic plate unit 31 is excited and magnetically reacts with magnetic element 24, driving impeller 2 to rotate relatively to fan frame 1. Moreover, if it is desired to improve the performance of impeller 2, the height of magnetic element 24 along an axial direction of the fan may be smaller than the thickness of magnetic plate unit 31 along the axial direction. Magnetic element 24 includes an outer circumferential face having a central portion M1 along the axial direction of the fan. Magnetic plate unit 31 includes an inner circumferential face having a central portion M2 along the axial direction. Central portions M1 and M2 are preferably aligned with each other in a radial direction of the fan.

In the axial direction of the fan, the bottom face of shaft-coupling portion 11 of fan frame 1 is spaced from the top face of hub 21 of impeller 2 at a height (A), and magnetic plate unit 31 of stator assembly 3 has a maximum thickness (B). In this embodiment, maximum thickness (B) is the distance between a bottom face of the lowermost magnetic plate to a top face of the uppermost magnetic plate of magnetic plate unit 31 along the axial direction. Maximum thickness (B) has a ratio over the height (A), which can be expressed as (B/A). FIG. 3 depicts the performance diagram of the fan wherein the fan has different ratios (B/A) with the height (A) fixed at 4.5 mm. FIG. 4 depicts another performance diagram of the fan wherein the fan also has different ratios (B/A) but the height (A) is fixed at 2 mm. It can be recognized from FIGS. 3 and 4 that the fan is able to output a proper amount of air with proper air pressure when the ratio (B/A) is from 0.1 to 0.6. In other words, the fan has a better performance when the ratio (B/A) is between 0.1 and 0.6. It is noted that when the ratio (B/A) is between 0.2 and 0.4 the fan is able to output a larger amount of air with larger air pressure, so that the fan has a further improved performance.

Based on this, the invention provides a method for determining the dimensional proportion of the motor components of a slim cooling fan wherein the motor of the fan has a radial air gap. In the first step, the method selects the ratio of a maximum thickness (B) of a motor to a height (A) of the motor as 0.1 to 0.6. Maximum thickness (B) is the maximum distance between the bottommost and uppermost faces of a magnetic plate unit of the motor along the axial direction. Height (A) is the distance between the bottom face of a shaft-coupling portion of a fan frame and the top face of a hub of an impeller along the axial direction. In the second step, the method determines the value of one of the height (A) and maximum thickness (B). In the third step, the method determines the value of the other one of the height (A) and maximum thickness (B) based on the selected ratio (B/A) of 0.1 to 0.6 as well as the previously determined value obtained in the second step. The height (A) is between 2 mm and 4.5 mm. In this manner, the proper dimensional proportion of the motor can be quickly and correctly determined. Advantageously, the slim cooling fan is able to output a proper amount of air with proper air pressure when equipped with the motor, achieving an improved cooling effect.

FIG. 5 shows a slim cooling fan having a radial air gap according to a second embodiment of the invention. The fan is comprised of a fan frame 1, an impeller 2 and a stator assembly 4. Both impeller 2 and stator assembly 4 are installed in fan frame 1. Stator assembly 4 is able to drive impeller 2 to rotate, thereby generating airflows. The fan in the second embodiment differs from that in the first embodiment in that stator assembly 4 is wound with an enamel copper wire in an axial direction of the fan.

Specifically, stator assembly 4 is comprised of an insulation sleeve 41, a coil unit 42, a magnetic plate unit 43 and a magnetic-inducing shaft tube 44. The enamel copper wire mentioned above is axially wound around a predetermined part of insulation sleeve 41. Magnetic plate unit 43 includes at least one magnetic plate which may be made of material with magnetic conductivity. The magnetic plate may be a silicon steel plate, for example. In this embodiment, magnetic plate unit 43 includes a plurality of magnetic plates arranged at two axial ends of insulation sleeve 41. The outermost magnetic plate of the plurality of magnetic plates may have an extension portion extending in an axial direction of insulation sleeve 41, so that the outermost magnetic plate may have a larger area for enhanced magnetic induction with magnetic element 24 of impeller 2. Magnetic-inducing shaft tube 44 is fixed in shaft-coupling portion 11 of fan frame 1. Shaft 22 of impeller 2 is rotatably disposed in magnetic-inducing shaft tube 44. Both magnetic plate unit 43 and insulation sleeve 41 are fitted around an outer periphery of magnetic-inducing shaft tube 44. Magnetic plate unit 43 has one end resting on a top face of shaft-coupling portion 11, such that the extension portion of magnetic plate unit 43 faces magnetic element 24 of impeller 2 when a radial air gap (G) is formed therebetween. Thus, when magnetic plate unit 43 is magnetically excited, magnetic plate unit 43 will have a magnetic reaction with magnetic element 24 of impeller 2, thereby driving impeller 2 to rotate relatively to fan frame 1.

In the structure of the above cooling fan, there is a height (A) between the bottom face of shaft-coupling portion 11 of fan frame 1 and the top face of hub 21 of impeller 2 in the axial direction of the fan. Height (A) is from 2 mm to 4.5 mm. In addition, there is a maximum thickness B′ between the bottommost and uppermost faces of a magnetic plate unit 43 of the motor in the axial direction. In this embodiment, maximum thickness B′ is the distance between a bottom face of the bottommost magnetic plate and a top face of the uppermost magnetic plate of magnetic plate unit 43 in the axial direction. Based on this, there is a ratio of maximum thickness B′ to height (A), which can be expressed as (B′/A). When the ratio (B′/A) is from 0.1 to 0.6, the fan is able to output a proper amount of air with proper air pressure. In addition, when the ratio (B′/A) is from 0.2 to 0.4, the fan is able to output a larger amount of air with larger air pressure, attaining a further improved performance of the fan.

In conclusion, the motor components of the fan are designed with a preferred dimensional proportion to ensure that the fan is able to output a proper amount of air with proper air pressure, attaining an improved performance of the fan.

In addition, the proposed method is able to quickly and correctly determine the proper dimensional proportion of the motor components of a cooling fan, ensuring that the cooling fan is able to output a proper amount of air with proper air pressure. Thus, improved performance of the fan is attained.

Although the invention has been described in detail with reference to its presently preferable embodiments, it will be understood by one of ordinary skill in the art that various modifications can be made without departing from the spirit and the scope of the invention, as set forth in the appended claims. 

What is claimed is:
 1. A cooling fan having a radial-air-gap motor, comprising: a fan frame having a shaft-coupling portion; an impeller having a hub, a shaft and a plurality of blades, wherein the shaft is connected to the hub and rotatably coupled with the shaft-coupling portion of the fan frame, wherein the plurality of blades is annularly arranged on an outer periphery of the hub, and wherein at least one magnetic element is arranged on an inner periphery of the hub; and a stator assembly having a magnetic plate unit, wherein the magnetic plate unit has a face facing and spaced from the at least one magnetic element by the radial air gap, wherein there is a height (A) between a bottom face of the shaft-coupling portion of the fan frame and a top face of the hub of the impeller along an axial direction, wherein the height (A) is between 2 mm and 4.5 mm, wherein there is a maximum thickness (B) between the bottommost and uppermost faces of the magnetic plate unit along the axial direction, and wherein a ratio of the maximum thickness (B) to the height (A) is between 0.1 and 0.6.
 2. The cooling fan having the radial-air-gap motor as claimed in claim 1, wherein the ratio of the maximum thickness (B) to the height (A) is between 0.2 and 0.4.
 3. The cooling fan having the radial-air-gap motor as claimed in claim 1, wherein the magnetic plate unit includes at least one magnetic plate.
 4. The cooling fan having the radial-air-gap motor as claimed in claim 3, wherein the magnetic plate unit includes a plurality of magnetic plates, and wherein the maximum thickness (B) is a distance between a bottom face of the bottommost magnetic plate and a top face of the uppermost magnetic plate of the magnetic plate unit along the axial direction.
 5. The cooling fan having the radial-air-gap motor as claimed in claim 1, wherein the at least one magnetic element has a height along the axial direction smaller than or equal to a thickness of the magnetic plate unit along the axial direction.
 6. The cooling fan having the radial-air-gap motor as claimed in claim 5, wherein the magnetic element includes an outer circumferential face having a first central portion along the axial direction, wherein the magnetic plate unit includes an inner circumferential face having a second central portion along the axial direction, and wherein the first and second central portions are aligned with each other in a radial direction.
 7. A method for determining the dimensional proportion of a motor of a cooling fan that has a radial air gap, comprising: selecting a ratio of a maximum thickness (B) of the motor to a height (A) of the motor as 0.1 to 0.6, wherein the maximum thickness (B) is a maximum distance between the bottommost and uppermost faces of a magnetic plate unit of the motor along an axial direction, and wherein the height (A) is a distance between a bottom face of a shaft-coupling portion of a fan frame of the motor and a top face of a hub of an impeller of the motor along the axial direction; determining the value of one of the height (A) and the maximum thickness (B); and determining the value of the other one of the height (A) and the maximum thickness (B) based on the range of the ratio (B/A) and the previously determined value, wherein the height (A) is between 2 mm and 4.5 mm.
 8. The method for determining the dimensional proportion of the motor of the cooling fan as claimed in claim 7, wherein the range of the ratio (B/A) is 0.2 to 0.4. 